Diamond has drawn attention as a semiconductor device material because of its potential superior semiconductor property as well as mechanical, chemical, and thermal properties. Especially, because diamond has a band gap of about 5.5 eV at room temperature, it is expected to serve as a ultraviolet ray emitting device or an electron emitting device using negative electron affinity. Further, because of its high dielectric breakdown resistance, diamond is expected to serve as a high power device. Furthermore, because of its strong crystallinity, diamond is expected to serve as a device having high resistance to severe environmental condition especially used under a harsh condition such as high temperature or radiation.
Power devices using diamond have been well developed in recent years, and there have been some reports regarding a Schottky barrier diode having a Schottky junction, a device having a combination of a pn junction and the Schottky junction, a device having a pin structure, or the like. However, it is especially difficult to stably control a uniform impurity concentration or high crystallinity in the formation of an n-type diamond semiconductor layer. Therefore, a method for stably forming the n-type diamond semiconductor layer has been desired.